The objective of this study is to evaluate combination treatment regimens consisting of ddI/Nelfinavir/Ritonavir (Arm A) and d4T/ Nevirapine/Nelfinavir (Arm B) with respect to change in plasma HIV-1 RNA copy number from baseline to week 48. Other aims are: to evaluate the safety and tolerance of ddI/NFV/RTV (Arm A) and d4T/NVP/NFV (Arm B) based on laboratory and clinical toxicities and to evaluate individual pharmackokinetics and drug interactions in: the first 8 children in Arm A: ddI/NFV/RTV>.